This invention relates to custom-fitting iron-type golf clubs to a particular golf player, and to a unique sole-tape for use in club fitting, and method for using that unique sole-tape.
Since different individual golfers will have different height, leg length, arm length, body configuration, swings, and swing actions, it is well known that to function properly, golf clubs should be xe2x80x9cfittedxe2x80x9d to the individual player. Proper fitting will result in a xe2x80x9cprescriptionxe2x80x9d which will uniquely characterize a particular set of golf clubs so that they will function properly when hit by the golfer whom that prescription fits. Among the variables which may be specified in such a golf club prescription are total club length, shaft type and flex, grip size, golf club head design and lie angle.
The present invention is particularly focused on an improvement in fitting the lie angle of iron-type golf clubs. A face view of the club head 10 of an iron-type golf club is illustrated in FIG. 1, which also shows the xe2x80x9clie anglexe2x80x9d of that club head, which is the angle 11 defined between the horizontal ground plane H and the axis 12 of the hosel 13 and/or shaft 14 of the club, when that axis lies in a vertical plane which is perpendicular to another vertical plane, which is perpendicular to the club face and corresponding to straight lines of flight from the club face in the direction of a desired shot hit from that club face, i.e., a so-called target line plane. In the illustration of FIG. 1, that target line plane would be perpendicular to the paper on which FIG. 1 is drawn and emerging out of the paper toward the reader from the center of the illustrated club face. It will be appreciated that by tilting the club shaft and hosel somewhat upwardly or downwardly as indicated by arrows 15, the lie-angle will increase or decrease, respectively, and the xe2x80x9cliexe2x80x9d of the sole 16 of the club will be varied vis-a-vis horizontal plane H, which corresponds to horizontal turf upon which would lie a ball to be hit by the club head.
If a golf club is properly fit for a given player, when the club is swung by that player using his typical swing, at or about the point of ball impact the sole of the club will also impact the turf. The sole of most golf clubs is at least slightly curved from toe 17 to heel 18 of the club head, defining so-called xe2x80x9csole radius,xe2x80x9d and also is curved or rounded in the fore to aft direction, that is from the leading edge 19 of the sole to the trailing edge 20 of the sole as illustrated in bottom view FIG. 2, this curvature corresponding to a so-called xe2x80x9cbounce radiusxe2x80x9d or xe2x80x9csole camber.xe2x80x9d A properly fitted iron-type golf club should impact the turf at about the middle of the length of the sole if the lie angle is properly fitted.
In the past, fitting of the lie angle of an iron-type golf club has been facilitated by using either a plain sole tape or a tape partitioned into small squares, with one side of the small squares lying substantially parallel to the leading edge of the sole of an iron upon which the sole-tape is being used. The sole-tape is used by temporarily, usually for no more than one shot, applying the tape, which comprises an adhesive-backed thin film applied temporarily to cover substantially the entire area of the sole of an iron-type golf club being fitted to a particular golfer. Once applied, the golfer then hits a ball from a relatively hard surface which leaves a test scar on the tape evidencing that portion of the sole of the club which impacted the hard surface at or about the time the club head also hit the ball. The resultant test scar may be located anywhere along the heel to toe length of the sole-tape. As suggested above, the preferred location of the scar is in the middle of the sole, although it is common for the scar to be located off-center toward the heel or toe of the club thus indicating an ill-fitted club for the golfer who used it in creating the scar.
The forms of prior sole-tapes included those partitioned into small squares as an attempt to correlate test scar location with re-fitting the particular golf club head to the body and swing of a particular golfer. In use, the resultant test scar on such a sole-tape is supposed to be located in a square section of the tape that corresponds to a particular lie angle re-fitting specification.
However, even with prior art sole-tapes partitioned into small squares, which squares are correlated to proposed changes in lie angle, there remain other inherent uncertainties in the use of such sole-tapes for fitting of lie angle of iron-type golf clubs. For example, as the face angle, i.e., heel to toe direction, of the club face changes from any orientation other than square, that is perpendicular to the target line plane, the relationship between the lie of the sole of the club vis-a-vis the underlying turf or surface will be affected. If a test shot using a lie tape is hit with an open (slice) face, the position of the test scar on the lie tape will be distorted and mislocated vis-a-vis a preferred central scar location. Similarly, the test scar created by a shot executed with a more closed (hook) club face will likewise be a scar whose position on the lie tape will be erroneously located vis-a-vis a desired centrally located scar. The erroneous location of test scars on lie-angle fitting sole-tapes, and erroneous correlations between square markings on such prior tapes result in the production or re-fitting of the lie angles of iron-type golf clubs which is still substantially incorrect and ineffective.
The present invention is designed to overcome such shortcomings and defects in prior art lie-fitting sole-tape systems. In the present invention, the sole-tape is specially marked with gradation or graduation markings which are not merely lines perpendicular to the leading edge of the sole of the club, or squares including such lines, but are curved lines wherein the ends of each such gradation line where each such gradation line intersects the leading edge and trailing edge, respectively, of the sole of the club are closer to the toe and farther from the heel of the club than the center portions of those lines. This special form of curved gradation or graduation line adapts the gradation line so that it still properly correlates to a desired degree of correction of lie angle even when a test scar located on or adjacent that gradation line on a sole-tape after club testing may indicate that the particular test scar was created by a swing in which the face of the club was too closed or too open at the time of ball impact and test scarring, or the entire club head was tilted too far backward or tilted too far forward, that is too upright, at the time of the test swing and creation of the test scar. When the advantageous graduated sole-tape of the present invention is used, it is typically unnecessary to make further corrections in correlation between the lie-angle corrections suggested directly by the marking on the sole-tape corresponding to the specially shaped curved gradation lines, as often was the case with prior art sole-tapes.